JPS60183974A - Power source - Google Patents

Abstract

PURPOSE:To suppress a spike noise by composing a resonance circuit by adding a capacitor to the primary side winding of a high frequency transformer, and connecting an inductance in series with the secondary side winding. CONSTITUTION:A coil L is connected in series with one end of the secondary side winding W3 of a high frequency transformer T2. This coil L has a function of breaking a load R6 of the secondary side in a high frequency manner. Accordingly, the primary side winding W1 and the capacitor C7 connected with the both ends are resonated irrespective of the ON and OFF of a diode D2 due to a high frequency signal presented at the secondary side winding W3, a voltage waveform at the collector of a transistor Tr does not become rectangular but becomes a quasi-sinusoidal wave, thereby suppressing the spike voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a power supply device, and more particularly to a switching power supply.

(Background Art) A so-called switching power supply that converts commercial AC power to a higher frequency and rectifies the output of a high-frequency transformer and its secondary winding to obtain a desired DC voltage has a small size.
It has become widely used because it has many advantages such as high efficiency and light weight.

FIG. 1 is a circuit diagram of a conventional switching power supply, commonly referred to as a square wave switching power supply. In the figure, 1-1' is an input terminal to which a commercial power source (not shown) that rectifies commercial AC voltage to form DC voltage is connected. TI is a high-frequency transformer, and the negative side winding W
, , W2 and a :43 wire W3 on the secondary side, and the polarity of each is set as shown in the figure. A capacitor C is installed in the winding WI to absorb the high voltage spike voltage that occurs.
3 and resistor R2 are connected in series. @3 One end of the wire W2 is connected to the base of the transistor Tr via a constant circuit consisting of a resistor R5 and a capacitor C4 that determines the switching period of the transistor Tr, and the other end is connected to the emitter of the transistor Tr (7). ing. Secondary winding W3 is connected to load resistor R6 via diode D2.

Rj and R,1 are bias resistors, and C1 and C are smoothing capacitors.

The operation of this circuit follows blocking oscillation. That is,
The DC voltage applied to the input terminal 1-1' is converted into a square wave voltage at a period determined by the time constant of the resistor R1 and the capacitor C7+. The reason for using a square wave is to minimize the collector loss of the transistor Tr. That is, this is the case when the transistor Tr is operated at class 0 and the collector voltage becomes the collector saturation voltage of the transistor Tr while the collector current is flowing, and a square wave easily satisfies this condition.

However, such a switching power supply has a problem in that when converting a DC voltage to a high frequency, a square wave is used as the high frequency as described above, and therefore extremely large spike-like noise is generated. Such spike voltages result in large noise B, and are not only unsuitable for precision sources, but also for general audio equipment, etc., and as they become more diversified, the influence of noise on peripheral equipment can be ignored. It's gone.

Here, in the circuit shown in FIG. 1, the high frequency transformer T
A resonant capacitor is loaded on the winding W1 of the transistor Tr, and by using this resonance, the operation of the transistor Tr is 0 class and a sine wave.
It is conceivable that the power supply is configured to suppress the spike voltage. However, this configuration requires the transistor T
When r is on and the regulating tQ diode D2 connected to the secondary winding W3 of the high frequency transformer T1 is on, the winding W1 of the high frequency i lance T is short-circuited and a low impedance is connected in parallel. Normally, in this condition 1, the winding W1 cannot have resonance characteristics, so it was difficult to realize.

In this way, the spike noise of a switching power supply is generated because the converted high frequency is a square wave, has an extremely wide frequency spectrum, and is the worst noise to avoid.

FIG. 2 is a circuit diagram in which the switching power supply is a half-sine wave, and when there is no coil as shown in FIG.
The applicant has proposed a switching power supply in which the anodes of In the following description, a state in which there is no coil will be described.

In the same figure, T is a high frequency transformer, and windings Wl and W2
The primary side has a winding W3, and the secondary side has a winding W3. The polarities of windings Wl and W3 are set as shown in IA. This is half-wave rectification using the diode D2 on the secondary side, and in this case, by setting the polarities of the primary and secondary sides of the high-frequency transformer as shown, both the switching transistor Tr and the diode D2 are turned off. This is to eliminate one period. - A resonant capacitor C7 is connected to the 'Ij3 line W1 on the next side. Therefore, during the period when both the transistor Tr and the diode D2 are off, the primary winding WI of the high frequency transformer has a low impedance and is not short-circuited, and a resonant circuit is formed by the winding WI and the capacitor C7. Since the on and off times of the transistor Tr can be set approximately equal, in such a case, the converted high frequency becomes a half sine wave, and the transistor Tr is saturated during the period when the collector current is flowing. Collector loss is the lowest. Half IF
Unlike a square wave, a string wave has an extremely narrow frequency spectrum and a low high frequency level, so that noise generation can be extremely reduced compared to a square wave.

Next, the resistor R[(, capacitor C7, diode D3, and Zener diode D4 form an auto-bias circuit. In the auto-bias circuit, when the load R6 becomes smaller, the Q of the resonant circuit increases, As a result, the collector voltage of the transistor Tr is prevented from increasing.In other words, when the collector voltage increases, the 73 voltage of the winding W2 also becomes -H.This voltage is reversed to the transistor Tr via the capacitor 07 and the diode D3. Therefore, the bias becomes deeper and the collector current decreases, suppressing the previous rise in collector voltage.

However, in the case where the coil L is not present in FIG. 2, it is clear that double-wave rectification cannot be performed on the output side since the resonance characteristic occurs only when D2 is off. Of course, for half-sine waveform types, double-wave rectification is preferable to half-wave rectification.

(Objective of the Invention) The present invention has been made by focusing on such conventional problems, and provides a power supply device that can suppress the generation of spike noise and can perform double-wave rectification on the output side. The purpose is to

Hereinafter, the present invention will be explained based on embodiments and with reference to the drawings.

(Structure and operation of the invention) FIG. 2 is a circuit diagram of an embodiment of the power supply device according to the invention. The present invention is characterized by a coil connected in series to one end of the secondary winding W3 of the high frequency transformer T2. The coil has a function of blocking the load R6 on the secondary side at a high frequency. Therefore, regardless of whether the diode D2 is turned on or off due to the high frequency signal appearing in the secondary winding Wj, the negative winding W1 and the capacitor C7 connected to both ends thereof resonate. Therefore, the voltage waveform at the collector of the transistor Tr is not a square wave but a quasi-sine wave, and the generation of spike voltage is suppressed. Here, the e of C7 is preferably several thousand picofarads, and the i of L is preferably several microhenries to several tens of microhenries.The coil L also operates as a choke coil for alignment,
(Usually, a coil of several hundred microhenries is used for this function), further suppressing the generation of spike voltages. Furthermore, as mentioned above, since the diode D2 resonates when it is on and off, the output side, that is, the high frequency transformer T
Double-wave rectification is possible on the secondary side of 2.

Note that the other configurations are the same as in FIG. 2.

Next, the operation will be explained. The transistor Tr repeats on and off according to the voltage applied to the pace. The resonant circuit formed by the capacitor C7 and the winding W1 resonates both when it is on and when it is off, because the load on the secondary side is blocked at high frequency by the coil. As a result, an opposing high frequency signal also appears in the secondary winding W3, and a desired double-wave rectified and 1-smoothed output is supplied to the load R6 via the diode D2 and the smoothing capacitor C5.

Below-1-1 The present invention has been explained based on one embodiment. 6 As another embodiment of the present invention, for example, the transistor connected to the temporary side of the high frequency transformer T is push-pull, and the output side is double-wave rectified. Examples include those that perform

(Effects of the Invention) As described in 1-1 above, according to the present invention, it is possible to provide a power supply device in which the generation of spike noise is sufficiently suppressed and double-wave rectification is possible on the output side.

[Brief explanation of the drawing]

Figure 1 shows a circuit diagram of a conventional switching type power supply, and Figure 2 shows a circuit diagram of a conventional switching type power supply.
The figure is a circuit diagram of an embodiment of a power supply device according to the present invention. R1 to R,----resistor, C1 to C8--m-capacitor, L--11-coil, T,, T2--m-high frequency transformer. W, -W,---Single winding. Dl~D3---diode, D7+-m-zener diode, Tr--1 transistor. Special 1;1 Applicant TDC Co., Ltd. Patent Application Agent B1) Buried soil Megumi Yamaki

Claims (1)

[Claims] A means for rectifying and smoothing an AC commercial power source to obtain a DC voltage, a high-frequency transformer for converting the DC voltage into a high-frequency voltage, and a rectifying element to rectify and further smooth the high-frequency voltage converted to a desired value to obtain the desired value. A switching power supply device for obtaining a direct current voltage, characterized in that a capacitor is added to the primary winding of the high frequency transformer to form a resonant circuit, and an inductor is connected in series to the secondary winding.